This invention relates to a micro-pump (or miniature pump) that is suitable for use in biomedical and bio-analytical applications.
Micro-pumps have recently been of interest and found applications, for example, in the life sciences and the pharmaceutical sector. One application is the delivery of drugs to the human body. For this purpose, micro-pumps are worn on the human body or implanted therein. Micro-pumps are also used in bio-analytical or biochemical research.
One of the driving factors for the increase in bio-analysis applications is the completion of the Human Genome Project, which results in the rapid development of molecular diagnostics in the laboratories. Diagnostic systems used in these laboratories include micro-pumps which are essential for micro-fluid manipulation of reagent and fluid samples. These micro-pumps, with integrated micro-valves, are capable of precise and controllable fluid delivery in the range of μl/min to ml/min. To avoid contamination, most components in a diagnostic system, including micro-pumps, are typically disposed after each use. Consequently, a micro-pump for use in such a diagnostic system should ideally be low in cost, reliable and easy to control.
Various types of micro-pumps are available. Some of these micro-pumps are described in U.S. Patent Application 2002/0081866, Choi et al., “Thermally Driven Micro-pump Buried In A Silicon Substrate And Method For Fabricating The Same”; U.S. Pat. No. 6,390,791, Maillefer et al., “Micro Pump Comprising an Inlet Control Member For Its Self-Priming”; U.S. Pat. No. 5,759,014, Van Lintel, “Micro-pump”; U.S. Pat. No. 5,499,909, Yamada et al., “Pneumatically Driven Micro-pump”; U.S. Pat. No. 6,520,753, Grosjean et al., “Planar Micro-pump”; U.S. Pat. No. 6,408,878, Unger et al., “Microfabricated Elastomeric Valve And Pump Systems”; WO 02/43615, Unger et al., “Microfabricated Elastomeric Valve And Pump Systems”; Didier Maillefer et al., “A High-Performance Silicon Micro-pump For Disposable Drug Delivery Systems”, The thirteenth IEEE International Micro Electro Mechanical Systems (MEMS-2000) Conference, Miyazaki, Japan; Melvin Khoo et al., “A Novel Micromachined Magnetic Membrane Microfluid Pump”, The 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society. Chicago, IL, 2000; R. Linnemann, P. Woias, C. D. Senffl, and J. A. Ditterich, “A self-priming and bubble tolerant piezoelectric silicon micro-pump for liquids and gases”, The 11th annual international workshop on MEMS. 1998, Heidelberg Germany, pp.532-537; K. P. Kamper, J. Dopper, W. Ehrfeld, and S. Oberbeck, “A self-filling low-cost membrane micro-pump”, The 11th annual international workshop on MEMS. 1998, Heidelberg Germany, pp.432-437; Jun Shinohara et al., “A high pressure-resistance micro-pump using active and normally-closed valves”, Thirteenth IEEE International Micro Electro Mechanical Systems (MEMS-2000) Conference. Miyazaki, Japan, 2000; Charles Grosjean et al., “A thermopneumatic peristaltic micro-pump”, Technical Digest of Transducers '99, Sendai, Japan; and Didier Maillefer et al., “A high-performance silicon micro-pump for an implantable drug delivery system”, The 1999 IEEE International Micro Electro Mechanical Systems (MEMS1999) Conference. Orlando, Fla., USA, 1999.
Some of the micro-pumps generally include a diaphragm in a chamber that is bounded either by two check valves or two nozzle/diffuser configurations. Such micro-pumps are disclosed in U.S. Pat. No. 5,759,014, 6,390,791, and Didier Maillefer et al., “A High-Performance Silicon Micro-pump For Disposable Drug Delivery Systems”, The thirteenth IEEE International Micro Electro Mechanical Systems (MEMS-2000) Conference, Miyazaki, Japan. The diaphragm of these micro-pumps is typically fabricated from a silicon wafer using bulk micro-machining or surface micro-machining. Bulk micro-machining is a subtractive fabrication method whereby single crystal silicon is lithographically patterned and then etched to form three-dimensional structures. Surface micro-machining is an additive method where layers of semiconductor-type materials such as polysilicon, silicon nitrate, silicon dioxide, and various suitable metals are sequentially added and patterned to make three-dimensional structures. The use of either of the above methods requires clean room facilities and careful quality control processes. Consequently, the micro-pumps including the silicon diaphragm are high in material cost and expensive to manufacture. The high cost may be prohibitive for disposable use. A cheaper alternative to these micro-pumps is thus desirable, especially for disposable use in bio-analysis applications.
Furthermore, the silicon diaphragm has a very high Young's modulus of about 100 Gpa. A micro-pump having such a diaphragm generally has a low compression ratio, which is defined by:ε=(ΔV+V0)/V0                 where ΔV is the stroke volume, and                    V0 is the dead volume, which is a volume of fluid that is not displaced in a pumping chamber during a pumping cycle.                        
A low compression ratio is disadvantageous for a micro-pump where self-priming is concerned. To achieve self-priming in a micro-pump, i.e. to be able to pump as much gas and gas bubbles out of the micro-pump, the compression ratio needs to be maximized. To maximize compression ratio, the dead volume must be minimized while the stroke volume maximized. This maximizing of a stroke volume of a micro-pump having a silicon diaphragm is not easily achieved, especially if the micro-pump has a pumping chamber with angular profiles and/or the diaphragm is driven with an actuator, such as a piezo element that is capable of generating only a limited actuation force. Such a micro-pump may exhibit a relatively large dead volume due to a mismatch between the shapes of the silicon diaphragm and the pumping chamber.
K. P. Kamper, J. Dopper, W. Ehrfeld, and S. Oberbeck, “A self-filling low-cost membrane micro-pump”, The 11th annual international workshop on MEMS. 1998, Heidelberg Germany, pp.432-43, discloses a micro-pump having a layered construction that has a relatively high compression ratio. This micro-pump includes top and bottom molded polycarbonate housing parts that include microstructures formed therein that serve as inlet and outlet valves and alignment structures. A polycarbonate valve membrane separates the top and bottom parts. The micro-pump also includes a pump membrane, which is separate from the valve membrane. The pump membrane is mounted on top of the upper housing part. Fluidic connection between a space underneath the pump membrane and a valve plane where the valve membrane is located is achieved by two cylindrical through-holes in the upper housing part.